The subject matter disclosed herein relates to structural health monitoring of materials, and more specifically, to systems and methods for structural health monitoring using nuclear quadrupole resonance.
In general, nuclear quadrupole resonance (NQR) spectroscopy is a chemical analysis method for obtaining information relating to the local environment surrounding certain atoms and, more specifically, certain nuclei. For example, nuclei that have a quantum spin number greater than ½ can have an electric quadrupole moment. The electric quadrupole moment can be affected by a nucleus' local electronic environment, such as the nature of certain chemical bonds in the vicinity of the nucleus, and also by ionized atoms in the vicinity of the nucleus. The quadrupolar nuclei, as a result of their electronic environment, exhibit certain energy states. The differences between these energy states often fall in the range of the radiofrequency (RF) portion of the electromagnetic spectrum. Therefore, in a similar manner to nuclear magnetic resonance (NMR) spectroscopy, NQR spectra may be obtained nondestructively with an RF receiver, such as an RF coil.
However, unlike NMR, which uses a static magnetic field to align the electric dipole of certain gyromagnetic nuclei (e.g., those having quantum spin numbers of ½), NQR relies on the local electronic environment surrounding the quadrupolar nuclei to orient the nuclei in certain directions. In this way, NQR can be especially sensitive to the local electrical environment surrounding the quadrupolar nuclei. Other factors that can affect an NQR spectrum of a given nucleus include the temperature and/or the crystalline state of a sample having the nucleus of interest. Therefore, the NQR spectrum of a given nucleus within a sample may vary from location to location, depending at least on chemical environments, local crystal structures, temperature variations, and so forth.